Polymer-zinc corrosion inhibiting method

ABSTRACT

Use of low molecular weight polymers and zinc to inhibit the corrosion of metals by oxygen-bearing waters.

United States Patent [1 1 Hollingshad et a1.

[ POLYMER-ZINC CORROSION INHIBITING METHOD [75] Inventors: William Robert Hollingshad, Bethel Park; Paul Hotchkiss Ralston, Pittsburgh, both of Pa.

[73] Assignee: Calgon Corporation, Pittsburgh, Pa.

[22] Filed: June 4, 1973 [21] Appl. No.: 367,083

[56] References Cited UNITED STATES PATENTS 3,578,589 5/1971 l-lwa 2l/2.7 R

[ 51 May 27, 1975 3,663,448 5/1972 Ralston 21/2.7 R 3,669,615 6/1972 Murray 2l/2.7 R

3,669,616 6/1972 Murray 2l/2.7 R

3,709,815 1/1973 Boothe t 252/180 3,709,816 l/1973 Walker 252/180 3,723,333 3/1973 Freyhold 21/27 R 3,752,761 8/1973 Boothe 4. 252/180 3,766,077 10/1973 Hwa 21/2.7 R 3,816,333 6/1974 King 21/2.7 R

Primary Examiner-Benjamin R. Padgett Assistant Examiner-Donald P. Walsh Attorriy, Agent, or Firml-1arry 'E. W'estlakej' Rudolph J. Anderson; Martin L. Katz [5 7 ABSTRACT Use of low molecular weight polymers and zinc to inhibit the corrosion of metals by oxygen-bearing watGI'S.

4 Claims, N0 Drawings 1 POLYMER-ZINC CORROSION INHIBITING METHOD BACKGROUND OF THE INVENTION This invention relates to the inhibition of corrosion in water systems which utilize oxygen-bearing waters.

More particularly. this invention relates to the use of compositions comprising low molecular weight polymers and zinc to inhibit the corrosion of metals in water systems which contain oxygen-bearing waters.

Oxygen corrosion is. of course. a serious problem in any metal-containing water system. The corrosion of iron and steel is of principal concern because of their zothiazole may be added to the final formulation in varying amounts to improve its usefulness in a wider variety of industrial applications where both steel and copper or its alloys are present in the same system.

The following table illustrates the effectiveness of polyacrylic acid (molecular weight about 1,000) and a partially hydrolyzed polyacrylamide (molecular weight about 7,000) when used with and without zinc at the dosages and pH indicated.

The test procedure used was a standard 5-day continuous immersion, mild agitation test carried out in synthetic Pittsburgh tap water for 5 days (95F). Steel corrosion rates are noted in the following table:

extensive use in many types of water systems. Copper TABL and its alloys, aluminum and its alloys. and galvanized E l steel are also used in water systems and are subject to w h /L C v R D f I erg t oss orrosion atc ata or Corroslon' N? h qlscovfired no\el .conioblon mhlbl' Polymers of Polyacrylic Acid and Partially Hydrolyzcd tors which will inhibit oxygen corrosion in water sys- Polyacryla mide With and Without Zinc tems containing such metals. P Partially SUMMARY OF THE INVENTION Polyacrylic Corrosion +a We have found that compositions comprising low Aud (ppm) Zn Rnemdd) PH molecular weight polymers and zinc are effective cor- 0 (i u 200 7.2-7.4 0 l0 0 143 6.6-7.0 rosion inhibitors. Suitable polymers include water- 0 m m 14 h 2:) soluble salts of acrylic acid, acrylates, methacrylates, o 0 l52 (i l6.l

3o 0 l0 :3 unhydrolyzed or partially hydrolyzed acrylamides, and

i n e The 01 mers acnlsmdomethyl profane iulfo at y The following table illustrates the influence of the may or p0 ymers o 0 e a w 30 ratio of polymer to zinc on several corrosion-inhibiting mennomd polymers and may have a molecular weght compositions of this invention. These tests were run in of from about 500 to about The Preferred synthetic Pittsburgh water. Steel electrodes were used lficulflr Weight, however, is about 0 Suitable Waterin polarization test cells with the initial pH at 7.0. Inhibsoluble salts include the alkali metal. alkaline earth concentrations were l l d on h b i h metal, Zinc, Cobalt, ammonium of ino and o e 81- tive material. The amount of corrosion that had taken kanol amine salts. place was determined from the current density at the The zinc ion may be supplied in many ways. For exintersection of an extrapolation of the so-called Taa l the inc i n may be dd d b utili i a w fel: portion of the anodic polar zation curve with the soluble zinc salt, such as, zinc chloride, zinc acetate, 40 equlllbnum imlxed. Potential Value, y zinc nitrate. and zinc sulfate, which forms zinc ions in ffirred to as COYTOSIOH P a E nrf. Applicaaqueous solution. The zine ion may also be supplied by non of Faljaday S allows a computmon of dlrect t mathematical relationship between the current density adding zinc ust to a solution of the polymer.

at Em. expressed in amperes per square centimeter Our corrosion-inhibiting compositions can contain a and a more useful corrosion rate expression such as ratio of polvmer to zinc of from about 1:3 to about 5:1

. f d h V f m I bout milligrams of steel consumed per square deeimeter of by welght' 8 errc rano Is f surface per day (m.d.d.) and mils per year (m.p.y.). 3:1 b 1 hese COmpOSmOnF e This relationship is such that a current density value of tively inhibit corrosion of metals when maintained in a -1 amperes/cmzxl mg/dmz/day Further the water system ataconcentration of at least about 1 ppm value is calculated from the usual formula. at the above ratios and, P y about 5 to 50 PP m.p.y.Xm.d.d. 1.44/density, using a density value of Maximum concentrations a determined y the 7.87 g/cm for steel. The corrosion rate for steel in this nomic considerations of the particular applicati nwater without inhibitor is 100 mdd. This control value Compounds such as benzotriazole or mercaptobenapplies to both Tables 2 to 3.

TABLE 2 Weight Ratio Polymer to Zinc 1 2 l 1 l Polymer Dosage (mg/l) 10 100 I0 30 Polymer Used Polyacrylic Acid Sodium Polyacrylate Partially Hydrolyzcd Polyacrylamide The following table illustrates that the effectiveness of polymeric corrosion inhibitors decreases as the molecular weight increases.

TABLE 3 Polarization Corrosion Rate Data for Sodium Polyacrylates Approximate Dosages (mg/l) Corrosion Rate Molecular Weight Polymer Zinc (mdd) .000 I00 30 61 10,000 30 0 67 10,000 30 76 l0 000 I00 0 53 10,000 100 30 56 We claim:

1. A method of inhibiting the corrosion of metals in a water system comprising maintaining in the water of said system at least about 5 ppm of a composition comprising zinc and at least one low molecular weight polymer selected from the group consisting of polyacrylamide, poly acrylic acid and sodium polacrylate.

2. A method as in claim 1 wherein the polymer has a molecular weight of from about 500 to about 10,000.

3. A method as in claim 1 wherein the ratio of polymer to zinc is from about 1:3 to about 5:1 by weight.

4. A method as in claim 1 wherein the ratio of polymer to zinc is from about 3:1 to about 4:1. 

1. A METHOD OF INHIBITING THE CORROSION OF METALS IN A WATER SYSTEM COMPRISING MAINTAINING IN THE WATER OF SAID STSTEM AT LEAST ABOUT 5 PPM OF A COMPOSITION COMPRISING ZINC AND AT LEAST ONE LOW MOLECULAR WEIGHT POLYMER SELECTED FROM THE GROUP CONSISTING OF POLYACRYLAMIDE, POLY ACRYLIC ACID AND SODIUM POLACRYLATE.
 2. A method as in claim 1 wherein the polymer has a molecular weight of from about 500 to about 10,000.
 3. A method as in claim 1 wherein the ratio of polymer to zinc is from about 1:3 to about 5:1 by weight.
 4. A method as in claim 1 wherein the ratio of polymer to zinc is from about 3:1 to about 4:1. 